1. Field of the Invention
This invention relates to a system and method for displaying to a user of a canned gas (whether used as fuel, for breathing, or the like) the time remaining for use of the gas in the container.
2. The State of the Art
The afore-mentioned applications are directed to oxygen requirements for jet aircraft, and more specifically to determining, after an emergency depressurization, the proper flight level (FL; altitude to fly) to balance the the fuel reserve and the oxygen reserve under such conditions. After an emergency depressurization, if the plane can make an alternate airport at a FL100 (10,000 foot elevation), there is no need for emergency oxygen; only at higher flight levels is oxygen required. However, the higher a jet flies, the less fuel is required. So there is a balance between the amount of emergency oxygen and the amount of fuel in order for the plane to reach an alternate airport during an emergency.
One method for providing an indication to the pilot(s) of the oxygen remaining is to sense the pressure, and preferrably also the temperature, of the pressurized gas source. These measurements are then used, in combination with a microprocessor, to calculate the volume of gas (e.g., liters) in the gas container. As gas it used, the pressure and temperature of the source change; sampling of this information over time provides a lapse rate. Alternatively, an actual flow meter can be used to measure the flow of gas, and sampled over time via the microprocessor, a lapse rate can be determined. The combination of the lapse rate and the calculated amount of gas remaining provides an indication of the duration for which the remaining gas will last.
It is this duration which is the subject matter of the instant specification. Bottled compressed gas is used for various endeavors and in various industries: acetylene for welding; nitrogen for electron microscopes; oxygen (or modified oxygen, containing nitrogen and/or helium) for scuba and for firefighters; and hydrocarbons for domestic heating and hot water, for powering vehicles, and for cooking; among others.